(a) Field of the Invention
This invention relates to a transparent aqueous tin compound solution suitable for forming transparent conductive tin oxide and to a method of producing transparent conductive tin oxide using said aqueous solution.
(b) Description of the Prior Art
In recent years, accompanied with the remarkable development in the field of electro-optical elements, attention is paid to transparent conductive membranes of the type of SnO.sub.2 or In.sub.2 O.sub.3. They are actively developed, for example, as transparent electrodes of various optical devices such as those of electro-luminescence, liquid crystals, image accumulation devices, etc.; as heating elements or resistors utilizing their heat resistance and anti-abrasion properties; as solar cells uitizing their high conductivity; or as selective permeable membranes for use in solar heat electricity generation utilizing their high reflexibility in infrared.
Among the methods of forming these transparent conductive membranes are known:
(1) chemical vapor deposition methods, PA1 (2) vacuum evaporation method, PA1 (3) sputtering method, PA1 (4) coating method.
All of the above-mentioned methods (1)-(3) use complicated apparatus and are inferior in operability. In addition, they usually necessitate an etching step after membrane formation, to form a pattern.
In the method (4) also, when using an inorganic salt such as SnCl.sub.4 for example, since hydrogen chloride or other chloride gases are generated upon heat decomposion, severe corrosion of the apparatus takes place. Also, the chlorine remaining in the membrane may become a cause of impairing the conductivity. There are also methods of using organic acid salts such as octyl acid tin salt or an organic complex. But in these methods, there are problems such that the uniformity of the membrane is impaired upon heat decomposition or gelation of the coating liquid takes place. Moreover, they have defects such that the formed membrane is uneven, cloudy and is liable to get hurt.
We, the inventors, taking the above-mentioned problems of the prior art into account, carried on further studies, and as a result, we attained this invention.
The object of this invention is to provide a transparent aqueous tin compound solution which has no restriction or problem on the apparatus, has high applicability, and can finally form tin oxide having excellent transparency, uniformity, compactness and conductivity, in an industrially advantageous manner, and to provide a method of producing transparent conductive tin oxide by using said aqueous solution.